The University of Massachusetts Lowell graduated its largest class ever Saturday as freshman House Representative Lori Trahan urged the graduates to “get in the game.”

The more than 4,500 graduates — from 43 states and 113 countries — represented the fast-growing school’s most diverse class as well, according to Chancellor Jacquie Moloney during her remarks at the commencement ceremony for undergraduates.

The class marked the 12th year in a row a record-sized class has graduated from the school, which joined the UMass system in 1991, according to the university.

Trahan, who won the race for the Third District in November after an intense primary that went to a recount, began her career in politics working for Martin T. Meehan, who once held the same seat and is the president of the University of Massachusetts schools.

“I came to Congress at a pivotal moment in our nation’s history,” Trahan, who grew up in Lowell, told the graduates at the Tsongas Arena in Lowell. “On all fronts we are faced with tough choices — choices including the future health and stability of our climate, choices about how we treat and care for those less fortunate, and choices on how and when we fight for our values.

“Never has it been more important for us to take control of our fate. These choices will be made on your watch and we need you ‘at the gate,’” she said, referencing a suffragette slogan.

The representative, a Democrat, pointed to examples of young activists who led movements for change, including Representative John Lewis, a civil rights leader, and Parkland, Fla., high school students who founded March For Our Lives after 17 were killed in a shooting at their school last year.

“As someone who has seen up close and learned from the activism of the next generation, I know that I want you by my side as we tackle these problems,” she said.